Extend faq.using to discuss fork failures

Jon TURNEY jon.turney@dronecode.org.uk
Fri Nov 4 13:40:00 GMT 2011

On 03/11/2011 17:17, Corinna Vinschen wrote:
> Thanks for doing that.  I looks good to me, with just one exception.
>> +<listitem>Address space layout randomization (ASLR). Starting with
>> +Vista, Windows implements ASLR, which means that thread stacks,
>> +heap, memory-mapped files, and statically-linked dlls are placed
>> +at different (random) locations in each process. This behaviour
>> +interferes with a proper<literal>fork</literal>, and if an
>> +unmovable object (process heap or system dll) ends up at the wrong
>> +location, Cygwin can do nothing to compensate (though it will
>> +retry a few times automatically). In a 64-bit system, marking
>> +executables as large address-ware and rebasing dlls to high
>> +addresses has been reported to help, as ASLR affects only the
>> +lower 2GB of address space.</listitem>
> Starting with "In a 64-bit system" it's getting a bit weird:
> - Starting with 4.5.3, gcc marks executables as large address aware
>    automatically, so this is going to be a lesser problem over time.  Is
>    it worth to mention this at all?  I suppose so, but the user should be
>    pointed to peflags to tests for this property first for the given
>    reason.
> - Starting with Cygwin 1.7.10, the high address area will be used for
>    the application heap on 64 bit systems and large address aware
>    executables.  Mmaps are located there, too.  This in turn leaves more
>    room for DLLs in the normal 2 Gigs memory area.  Therefore I would not
>    like to suggest rebasing DLLs into the high address area at all.  This
>    should only be done by people who know what they are doing.  Usually
>    there should be enough space in the lower 2 Gigs, especially when heap
>    and mmaps are out of the way, and given that the more recent rebaseall
>    will not create an arbitrary 64K hole between DLLs anymore when
>    rebasing.

I think it would be simplest just to drop the sentence starting "In a 64-bit 

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